You can try to fight the ticket. But before you do, try to find out if the fine amount for 70 in a 45 and 80+ in a 45. You were most likely at about 70 (at the least) when the officer estimated your speed. If the fine amount is the same then there probably isn't a very good reason to fight the ticket. I know for a fact that if your defense is "I was speeding but I was only going 65mph!" you're going to lose.